Flying within sight of the Soviet Mir space station Tuesday, the Columbia astronauts finally coaxed a balky $50 million telescope pointing system into action and began around-the-clock science observations.

"It appears at this time we have a good healthy payload," said mission manager Jack Jones. "All the instruments are up and working, and all the pointing systems appear to be performing (normally) at this time. This is a very exciting moment for us. We've been working very hard."While the costly Instrument Pointing System's three star trackers will need careful attention and possibly some additional fine tuning, Jones said the mounting appeared to be working properly at last, setting the stage for around-the-clock studies of the most violent stars and galaxies in the cosmos.

But frustrating problems activating Columbia's "Astro-1" observatory have thrown the crew behind schedule, causing them to miss priceless astronomical targets.

"I have to tell you, it's a big goose egg," mission scientist Ted Gull said of the flight's science results over the first two days. "But . . . I think within the next day or two, we'll be over the 50 percent hump and observing effectively."

On board Columbia are Brand, 59, co-pilot Guy Gardner, 42, John "Mike" Lounge, 44, Robert Parker, 53, Jeffrey Hoffman, 46, and civilian astronomers Ronald Parise, 39, and Samuel Durrance, 47.